Heat treatment of chromium-free steel bearings



United States Patent No Drawing. Filed Sept. 15, 1961, Ser. No. 133,264 2 Claims. (Cl. 148-134) This application relates to steel bearings and their use.

Steel bearings are subject to heavy stresses at high temperatures. To attain satisfactory service under such condition, it has heretofore been regarded as essential that the bearings be formed of highly alloyed steels containing chromium which renders the steels quite expensive.

It is accordingly an object of this invention to provide economical, low cost steel bearings.

It is a further object to provide l-ow alloy steels which can be heat treated to produce a desirable microstructure for bearing use.

We have found that steel bearings attaining the foregoing objects can be produced from chromium-free hypereutectoid steels containing manganese, silicon and molybdenum within restricted ranges. The desired properties can be obtained within the following ranges:

. Percent Carbon .80 to 1.20 Manganese 1.50 to 2.00 Silicon .50 to .90 Molybdenum .35 to .60 Aluminum .05 maximum with the balance iron and residual impurities.

A preferred range within the foregoing is as follows:

Percent Carbon .95 to 1110 Manganese 1.55 to 1.90 Silicon .50 to .80 Molybdenum .35 to .45 Aluminum .05 maximum with the balance iron and residual impurities.

The desired microstructure may be developed in such steel by the following heat treatment:

(1) Normalize by heating to within the range of 1550 and 1650 F. and air cooling (2) Spheroidize by:

(a) Heating to between 1225 and 1275 F. and

holding for to hours (b) Raising temperature to 1375 to 1425 F. and

holding for 1 to 3 hours (0) Furnace cooling to 1225 to 1275 F. and holding in such range for 5 to 10 hours ((1) Cooling to 1220 to -1-240 F. and holding for 4 to 8 hours (e) Cooling to 1190 to 1210" F. and holding f r 4 to 8 hours (f) Cooling to 1170 to 1180 F. and holding for 1 to 3 hours (g) Air cooling to room temperature (3) Transform by air cooling from 1475 to 1575 F. A specific example of steel within the foregoing range This steel contained .03% residual nickel and 03% residual chromium.

This steel was deoxidized with aluminum at the rate of 2 pounds per ton and ingots formed therefrom were forged in the temperature range of 2100 to 1800 F. into rounds and slow cooled.

The forged steel was thereafter heat treated by the following steps to develop the desired microstructure and properties:

(1) Normalized by heating to 1600 F. and air cooled to room temperature (2) Spheroidized by:

(a) Heating t-o 1250 F. and holding for 8 hours (b) Raising temperature to 1440 FL and holding for '1 hour I (c) Furnace cooling to 1250" F. and holding for 8 hours (d) Cooling to 1230 F. (e) Cooling to 1200 F. (f) Cooling to 1180" F. (g) Air cooling to room (3) Transformed by:

(a) Austenitizing in the range of 1475 to 1575 F. (b) Air cooling to room temperature Ideal Diameter tests were made on this steel with the results shown in the following Table I:

and holding for 6 hours and holding for 6 hours and holding for 2 hours temperature The spheroidized specimens after aust-enitizing at 1525 and 1575 F. had ASTM grain size of 7 and a microstructure composed essentially of martensite. It had well distributed carbides providing bearings formed therefrom with good wear resistance.

It is accordingly seen that the hyperutectoid chromiumfree steels of this invention containing low amounts of manganese and molybdenum have such high hardenability that they will withstand stressing at temperatures above 300 F. for long periods and therefore are most suitable for bearing use.

While we have shown and described one specific embodiment of our invention, it will be understood that this embodiment is merely for the purpose of illustration and description and that various other forms may be devised within the scope of our invention, as defined in the appended claims.

We claim:

1. The method of producing steel suitable for bearings characterized by good wear resistance comprising producing substantially chromium-free steel containing Percent Carbon .80 to 1.20 Manganese 1.50 to 2.00 Silicon .50 to .90 Molybdenum .35 to .60 Aluminum .05 maximum with the balance iron and residual impurities, spheroidizing said steel by holding it at a temperature between 1225 and 1275 F. for 5 to 10 hours, raising the temperature to 1375 to 1425 F. and holding for 1 to 3 hours, cooling in a plurality of successive stages to below 1180 F. and holding at each stage and then transforming the steel to a microstructure composed of martensite and well distributed carbides by austenitizing in the range of 1475 and 1575 F. and air cooling.

2. The method of producing steel suitable for bearings en ee s characterized by good wear resistance comprising produc-. ing substantially chromium-free steel containing I Percent Carbon .80 to 1.20

Manganese 1.50 to 2.00 Silicon .50 to .90 Molybdenum .35 to .60 Aluminum .05 maximum with the balance iron and residual impurities, spheroidizing said steel by holding it at a temperature between 1225 and 1275 F. for 5 to .10 hours, raisin the temperature 'to-13-75 to 1425 F. and holding for 1 to 3 hours, c oling to between 1225 and 175'F. and holding for 5 to 10 hours, cooling to between 1220 and 1240 F. and holding for 4 1208 hours, cooling to between 1190 and 1210 F. and holding for 4 to 8 hours, cooling to 1170 to 1180 F.

and holding for 1 to 3 hours and then transforming the steel to a microstructure composed of martensite and well distributed carbides by heating to a temperature between 1475 and 1575 Fraud air cooling.

References Cited by theExaminer UNITED STATES PATENTS 1,278,207 9/18 Potter I 148-12 2,087,764 7/37 B onte a 14812 2,166,839 7/39 Conley 148134 2,413,602 12/46. Bonte 75l23 2,630,382 3/53 Wasserman 75l23 2,662,010 12/53 Ahles 75l23 2,344,500 7/58 Peras 148143 2,987,429 6/61 Smith 148-12 15 published by the A.S.M., 1935 1940 Revised Ed), pages 207-208 relied on. I

DAVID L RECK, Primary Examiner.

RAY K. WINDHA-M, Examiner. 0

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,194,698 July 13, 1965 Joseph R. Mitchell et a1,

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 13, for "175 F." read 1275 F.

Signed and sealed this 28th day of December 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. THE METHOD OF PRODUCING STEEL SUITABLE FOR BEARINGS CHARACTERIZED BY GOOD WEAR RESISTANCE COMPRISING PRODUCING SUBSTANTIALLY CHROMIUM-FREE STEEL CONTAINING 